1. Field of the Invention
The present invention relates to a tracheostomy cannula with the format and distribution of its components designed so as to prevent the so-called tracheo-innominate fistula and the smallest stimulus to the coupling reflex, and to allow the cannula to be easily cleaned.
2. Description of the Related Art
The immense majority of cannulas for tracheostomy follow a basic concept that, in itself, is the model most used today. The cannula consists of a curved tube which acts as a passage for air between the patient's trachea and the environment or an artificial respirator. Since it is often necessary to use positive inspiratory pressure by means of the above-mentioned respirators, this tube is enveloped at its caudal end by a small balloon inflatable with air or liquid, which, by adhering completely to the internal lining of the trachea by means of a cross-section of the trachea, prevents the air insufflated by the respirator from escaping into the environment and/or into the larynx and pharynx, so that air may be conducted to the caudal section of the trachea, the bronchi and pulmonary alveoli. Yet another function of this small balloon or "cuff" is to support the tube itself inside the trachea. The dimensions of the cannula vary a great deal, especially when considering pediatric models. However, for adults the limits are quite close, and the distance from the cranial edge to its distal (or caudal) extremity in an orthogonal projection parallel to the axis of the trachea is on the order of 4 to 5.5 cm. in usual models. This distance is represented by distance "x" in FIG. 1 of the invention, which will be described later.
For a better understanding of the development of the present invention, it should be noted that many complications of a tracheostomy depend on irritations caused by the tube itself and/or by the small balloon. Thus, the longer the cannula tube, the greater the stimulus to coughing and the harder it is to clean both the cannula and the trachea. However, the greatest aggravating factor of such cannulas are the lesions to the trachea walls and/or to structures contiguous to the trachea which are produced by the possible compression exerted on these tissues by the tube, mainly in its caudal extremity and/or by the small balloon, especially if the pressure in the trachea's interior is very high. Such lesions range from a simple ischaemia to real perforations, with resulting secondary complications that are essentially obstructive, infectious and/or hemorrhagic. Among the latter can be noted the so-called tracheo-innominate fistual - an abnormal passage between the trachea and the innominate artery through such perforations. This fearful intercurrent process may cause severe hemorrhages which, when they do occur, lead to a case fatality rate of over 92%. Its occurrence is intimately related to the dimensions of the cannula: the longer it is, the greater the risk to the patient. This risk is already uncommonly high since the distance from the upper limit of the second cartilagineous trachial ring-cranial limit of the great majority of tracheostomies, up to the upper crossing point of the trachea with the innominate artery is, on the average for adults, about 3.3 cm, whereas the same distance measured on the cannula to its caudal extremity is approximately between 4 and 5.5 cm, as mentioned above.
Another "inconvenience", not properly a complication, in the use of these tracheostomy cannulas of the prior art is the need for a tape to be fitted around the neck of the patient and tied to the proximal extremity of the cannula in order to hold and fix it in place. However, there is a known model on the North American market which, among other small improvements, does away with the use of tapes around the neck and lends itself to the prevention of this tracheo-innominate fistula. It consists of a simple tube placed between the skin of the neck and the anterior wall of the trachea, and it is fixed there by its proximal and distal edges. Since it does not progress caudally along the interior of the trachea, if it does not do away with, it greatly reduces the risk of the onset of this complication. This cannula only hides the tracheal stoma without, however, allowing the use of positive inspiratory pressure through artificial respirators, which renders its use impossible in various patients to be tracheostomized. Besides, it is difficult to remove them from the tracheal stoma and these may, although on a smaller scale, lead to infectious, obstructive or hemorrhagic complications.
In short, whatever the model to be considered, there is still the risk of irritation on the part of the components of the cannula of the prior art, and the consequences tend to be more severe the more caudally these components progress through the interior of the trachea.